The Evaluation and Statistics Core Component will provide consultation on design and sampling issues during the initial developmental phase of the program project, including advice on the final sample designs for the population and registrant samples and power calculations taking sample design into account when appropriate. This core will also be responsible for all aspects of sampling, data collection, data management, respondent registration, and tracking for all projects. It will also be responsible for working with all investigators in pretesting and developing final versions of all survey instruments. Through this core, all common data items will be tracked to ensure that they are maintained in a common format to allow comparability across projects. Data files and data documentation will be prepared, and a central data base to be used by all projects will be managed. Centralized data management will ensure that all analyses are based on the same data sets and will enhance the uniformity in the computerized variables across study analyses. In addition, this core will oversee all data analysis activities. Analyses will range from tests of main effects (e.g., analysis of variance, logistic regression, survival analysis, and random-effects models) to multivariate analysis using structural equation models. Senior statisticians will be assigned to each analysis and will work with the investigators to ensure that the analysis is completed and the methods and results are written up appropriately.